The valve is the control device of the fluid pipeline. Its basic function is to switch on or off the flow of the pipeline medium, to change the flow of the medium, to change the flow direction of the medium, to adjust the pressure and flow of the medium and to protect the normal operation of the pipeline equipment. A large number of industrial valves are used after the invention of the steam engine in Watts. In the last two or three decades, the demand for valves has been raised due to the needs in petroleum, chemical, power plants, metallurgy, ships, nuclear energy and aerospace, prompting people to study And the production of high parameters of the valve, the working temperature from -269 ℃ ultra-low temperature to high temperature 1200 ℃, or even up to 3430 ℃, working pressure from ultra-vacuum 1.33x10-8Mpa (1x10-1 mmHg) to ultra-high pressure 1460MPa, valve diameter from 1mm to 600mm, even up to 9750mm, the valve material from cast iron, carbon steel to the development of titanium and titanium alloys, high strength corrosion-resistant steel, the valve drive from the manual to the development of electric, pneumatic, hydraulic, programmable, Remote control. With the continuous development of modern industry, valve demand continues to grow, a modern petrochemical plant will need tens of thousands of a wide range of valves, valve usage. Frequent opening and closing, but often due to manufacturing, the use of selection, maintenance, improper operation, run, run, drip, leakage phenomenon, which led to the flame, explosion, poisoning, scalding, or cause poor product quality, energy consumption, equipment corrosion , Material consumption increased, environmental pollution, and even cut-off and other accidents have been uncommon, so people want to get high-quality valves, but also require the use of valves to improve the level of maintenance, then engage in valve operators, maintenance personnel and engineering and technical personnel , Put forward new requirements, in addition to careful design, reasonable selection, the correct operation of the valve, but also timely maintenance and repair of the valve so that the valve "run, run, drip," and all kinds of accidents to a minimum.